Something that I really enjoyed doing as a child was typing around on an old Sharp PC-1401 [0] calculator. To be honest, I completely forgot about that "machine" until I read this article. Heck, I didn't even google for it in 15-20 years.
The amazing thing about it was, that I had BASIC and so I taught (with the help of my dad) myself to write easy games on it (you know: Guess the number and such). I just right _now_ discovered that the thing has an RS-232 interface and you could use PEEK, POKE and CALL. Oh my, the missed opportunities; But hey I was just to young at that time.
I think I know what I'll do, when I get home for christmas: Grab that PC 1401 and try out the RS-232 to see what's possible. Good times.